Showing papers on "Denticity published in 2004"
Patent•
18 Aug 2004
TL;DR: In this paper, the use of transition metal complexes of formula (I) in organic light-emitting diodes has been discussed, with the condition that n is at least 1.
Abstract: The invention relates to the use of transition metal complexes of formula (I) in organic light-emitting diodes, wherein: M1 represents a metal atom; carbene represents a carbene ligand; L represents a monoanionic or dianionic ligand; K represents a neutral monodentate or bidentate ligand selected from the group consisting of phosphines, CO, pyridines, nitriles and of conjugated dienes that form a π-complex with M1; n represents a number of carbene ligands, whereby n is at least 1; m represents a number of ligands L, whereby m can be 0 or = 1; o represents a number of ligands K, whereby o can be 0 or = 1, and the sum n + m + o depends on the oxidation stage and coordination number of the metal atom used and on the dentation of the ligands carbene, L and K as well as on the charge of the ligands carbene and L, with the condition that n is at least 1. The invention also relates to an OLED containing these transition metal complexes, a light-emitting layer containing these transition metal complexes, OLED's containing this light-emitting layer, devices that contain an inventive OLED, and to special transition metal complexes containing at least two carbene ligands.
365 citations
TL;DR: In this paper, an attempt is made to systemise the role which bidentate phosphinamine (P,N) ligands play in asymmetric catalysis, and the ligands will be classified, not by the reaction to which their metal complexes have been applied, but by the nature of their donor atoms.
Abstract: In this review, an attempt is made to systemise the role which bidentate phosphinamine (P,N) ligands play in asymmetric catalysis. The ligands will be classified, not by the reaction to which their metal complexes have been applied, but by the nature of their donor atoms. In this manner the development of ligand architectural design can be more easily monitored. The asymmetric transformations to which metal complexes of these ligands have been applied include among others, palladium-catalysed allylic substitutions, copper-catalysed 1,4-additions to enones and rhodium-catalysed hydroboration of vinylarenes. Excellent enantioselectivities, regioselectivities and reactivities have been achieved in each of these processes.
319 citations
TL;DR: In this paper, it was shown that N-heterocyclic carbenes are much stronger electron donors than their ubiquitous C2-bound counterparts, and the Tolman electronic parameter for 1-isopropyl-2,4-diphenyl-3methylimidazolin-5-ylidene is 2039 cm-1.
290 citations
TL;DR: In this paper, the interaction of CO2 and H2/CO2 with pure β-Ga2O3 and Pd/β-Ga 2O3 (1% Pd) was studied by temperature-programmed reaction, between 323 K and 723 K at 0.1 MPa.
215 citations
01 Jan 2004
TL;DR: In this article, structural and spin transition aspects of the most important families of polymeric Fe(II) compounds are reviewed, which contain N-donor heterocyclic 1,2,4-triazole, 1-R-tetrazole and bis monodentate pyridine-like bridging ligands.
Abstract: In this chapter, structural and spin transition aspects of the most important families of polymeric Fe(II) compounds are reviewed. These coordination compounds contain N-donor heterocyclic 1,2,4-triazole, 1-R-tetrazole and bis monodentate pyridine-like bridging ligands. Recent results involving new series of polymeric compounds formed by the combination of organic and inorganic tetra- and dicyanometallate complex bridging ligands are also discussed.
185 citations
Journal Article•
TL;DR: In this article, structural and spin transition aspects of the most important families of polymeric Fe(II) compounds are reviewed, which contain N-donor heterocyclic 1,2,4-triazole, 1-R-tetrazole and bis monodentate pyridine-like bridging ligands.
Abstract: In this chapter, structural and spin transition aspects of the most important families of polymeric Fe(II) compounds are reviewed. These coordination compounds contain N-donor heterocyclic 1,2,4-triazole, 1-R-tetrazole and bis monodentate pyridine-like bridging ligands. Recent results involving new series of polymeric compounds formed by the combination of organic and inorganic tetra- and dicyanometallate complex bridging ligands are also discussed.
174 citations
TL;DR: This study suggests that the surface complexes change depending on pH, and the monoprotonated monodentate complex should be favored.
Abstract: Quantum mechanical calculations were applied to resolve controversies about phosphate surface complexes on iron hydroxides. Six possible surface complexes were modeled: deprotonated, monoprotonated, and diprotonated versions of bridging bidentate and monodentate complexes. The calculated frequencies were compared to experimental IR frequency data (Persson et al. J. Colloid Interface Sci. 1996, 177, 263-275; Arai and Sparks J. Colloid Interface Sci. 2001, 241, 317-326.). This study suggests that the surface complexes change depending on pH. Four possible species are a diprotonated bidentate complex at pH 4-6, either a deprotonated bidentate or a monoprotonated monodentate complex at pH 7.5-7.9, and a deprotonated monodentate complex at pH 12.8. In addition, reaction energies were calculated for adsorption from aqueous solution to determine relative stability to form a monoprotonated monodentate complex and a deprotonated bidentate complex. According to these results, the monoprotonated monodentate complex should be favored. Vibrational frequencies of the monoprotonated monodentate and deprotonated bidentate complexes were analyzed with electronic effects on the Fe-OP and H-OP bonds.
158 citations
Patent•
01 Nov 2004TL;DR: In preferred embodiments, a polydentate pore-sealing ligand is used to seal or repair pores damaged by plasma processing as mentioned in this paper, and the ligands are cross-linked after attachment to the dielectric.
Abstract: In preferred embodiments, a polydentate pore-sealing ligand is used to seal or repair pores damaged by plasma processing. The polydentate ligand includes bidentate ligands corresponding to the general formula X—CH 2 —(CH 2 ) n —CH 2 —X or X—Si(CH 3 ) 2 —(CH 2 ) n —Si(CH 3 ) 2 —X. The polydentate ligand also includes tridendate ligands corresponding to the general formula X—CH 2 —(CH 2 ) m (CXH)(CH 2 ) o —CH 2 —X or X—Si(CH 3 ) 2 —(CH 2 ) m (CXH)(CH 2 ) o —Si(CH 3 ) 2 —X. Alternative embodiments may include single or multiply branched polydentate ligands. Other embodiments include ligands that are cross-linked after attachment to the dielectric. Still other embodiments include a derivatization reaction wherein silanol groups formed by plasma damage are removed and favorable dielectric properties are restored.
154 citations
TL;DR: In this article, eight dinuclear Au(I)-carbene complexes have been synthesized from various imidazolium-linked cyclophanes and related acyclic bis(imidazilium) salts, by treatment of the imidazeolium salts with [Au(I)(SMe2)Cl] in the presence of a carboxylate base.
Abstract: Eight dinuclear Au(I)-carbene complexes have been synthesized from various imidazolium-linked cyclophanes and related acyclic bis(imidazolium) salts, by treatment of the imidazolium salts with [Au(I)(SMe2)Cl] in the presence of a carboxylate base. Single crystal structural studies showed that the Au(I)-carbene compounds contain dinuclear (AuL)2 cations in which a pair of gold(I) centres are linked by a pair of bridging dicarbenoid ligands. Interestingly, the structural studies revealed short Au⋯Au contacts of 3.0485(3)
A and 3.5425(6)
A in two of these complexes. NMR studies showed that the (AuL)2 cations constructed from the cyclophane-based ligands retain a relatively rigid structure in solution, whilst those of the non-cyclophane ligand systems are fluxional in solution. The electronic absorption and emission spectra of the complexes in solution at room temperature were recorded and the complex with the shortest Au⋯Au contact was found to emit intensely at 400 nm and more weakly at 780 nm upon excitation at 260 nm. The compounds with longer Au⋯Au separations were not emissive under these conditions.
153 citations
TL;DR: Metal complexes of the kefzol complexes have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus mirabilis.
Abstract: Kefzol (kzl), a β-lactam antibiotic, possesses various donor sites for interaction with transition metal(II) ions [Co(II), Cu(II), Ni(II) and Zn(II)] to form complexes of the type [M(kzl)2]Cl2 and [M(kzl)Cl], with molar ratio of metal: ligand (M:L) of 1:2 and 1:1 respectively. These complexes were prepared and characterized by physicochemical and spectroscopic methods. Their IR and NMR spectra suggest that kefzol potentially acts as a bidentate, tridentate as well as monoanionic tetradentate ligand. The complexes have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus mirabilis. The metal complexes were found to be more potent against one or more bacterial species than the uncomplexed kefzol.
151 citations
TL;DR: Two-coordinate copper(I) acetate and copper methyl complexes, bearing an N-heterocyclic carbene (NHC) supporting ligand, have been synthesized and structurally characterized, and the stability of the monodentate acetate has been examined by DFT calculations as mentioned in this paper.
TL;DR: The development of bulky monodentate alkoxide, chalcogenolate (ER, E = S, Se or Te), amide, pnictide (ER2 = N, P, As), alkyl, aryl and silyl ligands is briefly surveyed in this paper.
TL;DR: In this article, an oxo-centred structure, containing only bridging carboxylate groups, is proposed for the zinc Versatic complex, which is believed to be present in the organic medium as Zn4O(V)6.
TL;DR: In this paper, aqueous solutions containing Ni(II) and a series of structurally related carboxylic acids were analyzed using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Ni K-edge X-ray absorption fine structure spectrograph (XAFS).
TL;DR: In this paper, a new strategy for the preparation of chelating bidentate ligands, which involves just the mixing of two monodentates functionalized with complementary binding sites, was reported.
Abstract: We report a new strategy for the preparation of chelating bidentate ligands, which involves just the mixing of two monodentate ligands functionalized with complementary binding sites. In the current example, the assembly process is based on selective metal-ligand interactions, using phosphite zinc(II) porphyrins 1-6 and the nitrogen donor ligands b-i. From only 16 monodentate ligands, a library of 60 palladium catalysts based on 48 bidentate ligand assemblies has been prepared. The relatively small catalyst library gave a large variety in the selectivity of the alkylation of rac-1,3-diphenyl-2-propenyl acetate. Importantly, small variations in the building blocks lead to large differences in the enantioselectivity imposed by the catalyst (up to 97% ee).
TL;DR: In this paper, the physical principles that determine the carboxylate-binding mode in metalloproteins were elucidated by surveying the Protein Data Bank (PDB) and performing density functional and continuum dielectric calculations.
Abstract: Aspartate and glutamate side chains are unique among the 20 amino acids, in regard to possessing carboxylate groups that can bind the metal cation either monodentately (via one of the carboxylate O atoms) or bidentately (via both carboxylate O atoms). In this work, we elucidate the physical principles that determine the carboxylate-binding mode in metalloproteins by surveying the Protein Data Bank (PDB) and performing density functional and continuum dielectric calculations. The metal and its first-shell ligands are explicitly modeled and treated quantum mechanically, whereas the second-shell effects and the metal-binding site environment are implicitly taken into account. We systematically investigate the effect on the carboxylate denticity of (i) its immediate surroundings, (ii) the metal type and coordination number, (iii) the total charge of the metal complex, and (iv) the relative solvent exposure of the metal-binding site. The results suggest that the carboxylate-binding mode is determined by compet...
TL;DR: In this paper, the synthesis and reactivity of palladium acetate/trifluoroacetate complexes stabilized by the presence of N-heterocyclic carbene (NHC) ligands are described.
TL;DR: Bisphosphite 11 with a 2,2'-biphenol bridge was found to be the best overall ligand for asymmetric hydroformylation of allyl cyanide with up to 80% ee and regioselectivities (branch-to-linear ratio, b/l) of 20 with turnover frequency of 625 [h(-)(1)] at 35 degrees C.
Abstract: A series of mono- and bidentate phosphites was prepared with (S)-5,5‘,6,6‘-tetramethyl-3,3‘-di-tert-butyl-1,1‘-biphenyl-2,2‘-dioxy [(S)-BIPHEN] as a chiral auxiliary and screened in the asymmetric hydroformylation of allyl cyanide. These hydroformylation results were compared with those of two existing chiral ligands, Chiraphite and BINAPHOS, whose utility in asymmetric hydroformylation has been previously demonstrated. Bisphosphite 11 with a 2,2‘-biphenol bridge was found to be the best overall ligand for asymmetric hydroformylation of allyl cyanide with up to 80% ee and regioselectivities (branch-to-linear ratio, b/l) of 20 with turnover frequency of 625 [h-1] at 35 °C. BINAPHOS gave enantioselectivities up to 77% ee when the reaction was conducted in either acetone or neat but with poor regioselectivity (b/l 2.8) and activities 7 times lower than that of 11. The product of allyl cyanide hydroformylation using (R,R)-11 was subsequently transformed into (R)-2-methyl-4-aminobutanol, a useful chiral buildi...
TL;DR: 99mTc compounds can be prepared at the tracer level in one-pot procedures with L1 and L2 being concomitantly present and the corresponding second ligand can be used to influence the physico-chemical properties of the conjugate.
Abstract: Mixed ligand fac-tricarbonyl complexes of the general formula [M(L1)(L2)(CO)3]
(M = Re, 99(m)Tc, L1
= imidazole, benzyl isocyanide, L2
= 1H-imidazole-4-carboxylic acid, pyridine-2,4-dicarboxylic acid, pyridine-2,5-dicarboxylic acid) have been prepared starting from the precursors [M(OH2)3(CO)3]+. The complexes can be obtained in good yield and purity in a two-step procedure by first attaching the bidentate ligand followed by addition of the monodentate. 99mTc compounds can also be prepared at the tracer level in one-pot procedures with L1 and L2 being concomitantly present. This [2 + 1] approach allows the labeling of bioactive molecules containing a monodentate or a bidentate donor site. Examples given in here are N-(tert-butoxycarbonyl)glycyl-N-(3-(imidazol-1-yl)propyl)phenylalaninamide, 5-((3-(imidazol-1-yl)propyl)aminomethyl)-2′-deoxyuridine and 4-(5-isonitrilpentyl)-1-(2-methoxyphenyl)-piperazine as L1 and N-((6-carboxypyridine-3-yl)methyl)glycylphenylalanine as L2. The corresponding second ligand can be used to influence the physico-chemical properties of the conjugate. The crystal structures of [99Tc(OH2)(imc)(CO)3], [Re(OH2)(2,4-dipic)(CO)3], [Re(bic)(2,4-dipic)(CO)3] and [Re(im)(2,5-dipic)(CO)3] are reported.
TL;DR: In this article, the new phosphinopyridine ligands were used for the synthesis of paramagnetic Ni(II) complexes [NiCl2(P,N)] 9−11, respectively.
TL;DR: KGaA et al. as discussed by the authors investigated the use of phenyl 2-pyridyl ketone and oxime (2-py)CNOH in manganese benzoate chemistry.
Abstract: The use of phenyl 2-pyridyl ketone [(ph)(2-py)CO] and its oxime [(ph)(2-py)CNOH] in manganese benzoate chemistry has been investigated. The reaction of an excess of (ph)(2-py)CNOH with Mn(O2CPh)2·2H2O affords the mononuclear complex [MnII(O2CPh)2{(ph)(2-py)CNOH}2]·1.2H2O (1·1.2H2O) in high yield. The MnII ion is coordinated by two monodentate benzoates and two N,N′-bidentate chelating (ph)(2-py)CNOH molecules in a cis-cis-trans fashion. The comproportionation reaction between Mn(O2CPh)2·2H2O and NnBu4MnO4 (3:1) in the presence of (ph)(2-py)CNOH in MeCN/EtOH/CH2Cl2 leads to the isolation of the mixed-valent cluster [Mn8O2(OH)2(O2CPh)10{(ph)(2-py)CNO}4]· 4CH2Cl2 (2·4CH2Cl2) in about 55% yield. A second synthetic procedure that leads to pure 2 involves the reaction between the known starting material (NnBu4)[Mn4IIIO2(O2CPh)9(H2O)] and four equivalents of the oxime ligand in CH2Cl2. The centrosymmetric octanuclear molecule contains four MnII and four MnIII ions held together by two μ4-O2− ligands and two μ3-OH− ions to give the unprecedented [Mn8(μ4-O)2(μ3-OH)2]14+ core, with peripheral ligation provided by ten PhCO2− (two η1, four syn,syn η1:η1:μ2 and four η1:η2:μ3) and four η1:η1:η1:μ2 (ph)(2-py)CNO− ions. The 1:1 reaction between Mn(O2CPh)2·2H2O and the ketone (ph)(2-py)CO affords the trinuclear complex [Mn3(O2CPh)6{(ph)(2-py)CO}2] (3) in more than 80% yield. As judged from single-crystal X-ray crystallography, the complex adopts a linear structure with one η1:η2:μ2 and two η1:η1:μ2 benzoates spanning each pair of metal ions. The terminal MnII ions are capped by bidentate chelating (ph)(2-py)CO ligands. The three complexes have been characterised by IR spectroscopy. The CV study of complex 2 in CH2Cl2 reveals irreversible reduction and oxidation processes. The magnetic properties of 2 and 3 have been studied by variable-temperature dc magnetic-susceptibility techniques. As the temperature approaches zero, the value of the χMT product for 2 approaches zero and, thus, the octanuclear complex has an S = 0 ground state. This S = 0 ground state is explained in terms of the magnetic behaviour of the central, butterfly-like [Mn4III(μ3-O)2]8+ subcore. The results for 3 reveal weak antiferromagnetic coupling, with J = −2.7 cm−1 for adjacent MnII ions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
TL;DR: The novel mixed ferrocenyl aryl/alkyl triphosphine is thermally stable and insensitive to air or moisture, and its robustness allows aryL alkynylation at 10(-1) to 10(-4) mol % catalyst loadings with TONs up to 250,000.
TL;DR: The ligands tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (L1, potentially hexadentate) and bis[3]-pyrazyl-1yl]dihydroborates (L2, potentially tetradentate), which have been used to prepare ternary lanthanide complexes in which the remaining ligands are dibenzoylmethane anions (dbm).
Abstract: The ligands tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (L1, potentially hexadentate) and bis[3-(2-pyridyl)pyrazol-1-yl]dihydroborate (L2, potentially tetradentate) have been used to prepare ternary lanthanide complexes in which the remaining ligands are dibenzoylmethane anions (dbm). [Eu(L1)(dbm)2] is eight-coordinate, with L1 acting only as a tetradentate chelate (with one potentially bidentate arm pendant) and two bidentate dbm ligands. [Nd(L1)(dbm)2] was also prepared but on recrystallisation some of it rearranged to [Nd(L1)2][Nd(dbm)4], which contains a twelve-coordinate [Nd(L1)2]+ cation (two interleaved hexadentate podand ligands) and the eight-coordinate anion [Nd(dbm)4]− which, uniquely amongst eight-coordinate complexes having four diketonate ligands, has a square prismatic structure with near-perfect O8 cubic coordination. Formation of this sterically unfavourable geometry is assumed to arise from favourable packing with the pseudo-spherical cation. The isostructural series of complexes [Ln(L2)(dbm)2]
(Ln = Pr, Nd, Eu, Gd, Tb, Er, Yb) was also prepared and all members structurally characterised; again the metal ions are eight-coordinate, from one tetradentate ligand L2 and two bidentate dbm ligands. Photophysical studies on the complexes with Ln = Pr, Nd, Er, and Yb were carried out; all show the near-IR luminescence characteristic of these metal ions, with longer lifetimes in CD3OD than in CH3OH. For [Yb(L2)(dbm)2], two species with different luminescence lifetimes were observed in CH3OH solution, corresponding to species with zero or one coordinated solvent molecules, in slow exchange on the luminescence timescale. For [Nd(L2)(dbm)2] a single average solvation number of 0.7 was observed in MeOH. For [Pr(L2)(dbm)2] a range of emission lines in the visible and NIR regions was detected; time-resolved measurements show a particularly high susceptibility to quenching by solvent CH and OH oscillators.
TL;DR: The use of phosphoramidite ligands in the rhodium-catalyzed asymmetric conjugate addition of potassium organotrifluoroborates to various enones in the absence of water is described.
Abstract: The use of phosphoramidite ligands in the rhodium-catalyzed asymmetric conjugate addition of potassium organotrifluoroborates to various enones in the absence of water is described. A systematic search for effective catalysts has been performed by use of high-throughput screening methods. Initially, we have screened reaction conditions, catalyst precursors, and focused ligand libraries. In the next stage we have used the monodentate ligand combination approach, and finally we have made a library of 96 different phosphoramidites by parallel synthesis in the robot (instant ligand libraries) and have tested these in the vinylation of cyclohexenone (up to 88% enantiomeric excess, ee) and 4-phenyl-3-buten-2-one (up to 42% ee). Arylation of cyclohexenone by use of potassium phenyltrifluoroborate gave 3-phenylcyclohexanone with 99% ee.
TL;DR: The experimental data suggest that in all cases coordination of the dithiocarbamate ligand (ESDT) takes a place through the two sulfur atoms, the -NCSS moiety acting as a symmetrical bidentate chelating group, in a square-planar geometry around the M(II) ion.
TL;DR: In this paper, a series of bulky monodentate phosphoramidite ligands, based on biphenol, BINOL and TADDOL backbones, have been employed in the Pd-catalysed allylic alkylation reaction.
Abstract: A series of bulky monodentate phosphoramidite ligands, based on biphenol, BINOL and TADDOL backbones, have been employed in the Pd-catalysed allylic alkylation reaction. Reaction of disodium diethyl 2-methyl malonate with monosubstituted allylic substrates in the presence of palladium complexes of the phosphoramidite ligands proceeds smoothly at room temperature. The regioselectivities observed depend strongly on the leaving group and the geometry of the allylic starting compounds. Mono-coordination occurs when these ligands are ligated in [Pd(allyl)(X)] complexes (allyl=C3H5, 1-CH3C3H4, 1-C6H5C3H4, 1,3-(C6H5)2C3H3; X=Cl, OAc). The solid-state structure determined by X-ray diffraction of [Pd(C3H5)(1)(Cl)] reveals a non-symmetric coordination of the allyl moiety, caused by the stronger trans influence of the phosphoramidite ligand relative to X-. In all of these complexes, the syn,trans isomer is the major species present in solution. Because of fast isomerisation and high reactivity of the syn,cis complex, the major product formed upon alkylation is the linear product, especially for monosubstituted phenylallyl substrates in the presence of halide counterions. In the case of biphenol- and BINOL-based phosphoramidites, however, a strong memory effect is observed when 1-phenyl-2-propenyl acetate is employed as the substrate. In this case, nucleophilic attack competes effectively with the isomerisation of the transient cinnamylpalladium complexes. The asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate afforded the chiral product in up to 93 % ee. Substrates with smaller substituents gave lower enantioselectivities. The observed stereoselectivity is explained in terms of a preferential rotation mechanism, in which the product is formed by attack on one of the isomers of the intermediate [Pd[1,3-(C6H5)2C3H3](L)(OAc)] complex.
TL;DR: In this article, the authors focus on contributions made by their group which have led to the development of two approaches to such heteroleptic complexes both of which use [Ru(CO)2Cl2]n polymer as a key precursor.
TL;DR: The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties.
Abstract: The preparation, X-ray crystallography and magnetic inves- tigation of the compounds PPh4- (Cr(bipy)(CN)4)· 2C H3CN·H2 O( 1) (mononuclear), ({Cr(bipy)(CN)4}2Mn- (H2O)4)· 4H 2 O( 2) (trinuclear), ({Cr- (bipy)(CN)4}2Mn(H2O)2 )( 3) (chain) and ({Cr(bipy)(CN)4}2Mn(H2O))·H2O· CH3CN (4) (double chain) (bipy = 2,2'- bipyridine; PPh4 + = tetraphenylphos- phonium)are described herein. The (Cr(bipy)(CN)4) � unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2 )o r two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2 )o r two (3) water molecules building a dis- torted octahedral environment. In 4, two chains of 3 are pillared through in- terchain Mn-N-C-Cr links which re- place one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordi- nation modes of (Cr(bipy)(CN)4) � co- exist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behav- iour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between Cr III and Mn II through the single cy-
TL;DR: In this paper, the preparation and crystal structures of four MnII carboxylate complexes containing 2-pyridinealdoxime, (py)CHNOH, are reported.
TL;DR: The materials and methods reported here allow the assembly of robust surface organometallic structures in which the active sites behave as isolated species, even near saturation monolayer coverages, which makes possible the rational design and synthesis of a class of heterogeneous oxide catalysts with atomic-scale precision at the active site.
Abstract: Metallocalixarenes were grafted onto silica using a surface organometallic approach and shown to be active and selective catalysts for epoxidation of alkenes using organic hydroperoxides. Calixarene−TiIV precursors were anchored at surface densities from 0.1 to near-monolayer coverages (0.025−0.25 calixarene nm-2). Several spectroscopic methods independently detected calixarene−TiIV connectivity before and after epoxidation catalysis. Kinetic analyses of cyclohexene epoxidation confirmed that the active sites were anchored on the silica surface and were significantly more active than their homogeneous analogues. The steric bulk and multidentate binding of the calixarenes led to structural stability and to single-site behavior during epoxidation catalysis. Rate constants were independent of surface density for cyclohexene epoxidation with tert-butyl hydroperoxide (11.1 ± 0.3 M-2 s-1) or cumene hydroperoxide (25 ± 2 M-2 s-1). The materials and methods reported here allow the assembly of robust surface organ...